The present invention relates to the arts of nuclear medicine and diagnostic imaging. It finds particular application in conjunction with gamma cameras and will be described with particular reference thereto. It is to be appreciated that the present invention is applicable to single photon emission computed tomography (SPECT), positron emission tomography (PET), whole body nuclear scans, and/or other like applications.
Diagnostic nuclear imaging is used to study a radionuclide distribution in a subject. Typically, one or more radiopharmaceuticals or radioisotopes are injected into a subject. The radiopharmaceuticals are commonly injected into the subject""s blood stream for imaging the circulatory system or for imaging specific organs which absorb the injected radiopharmaceuticals. Gamma or scintillation camera detector heads, typically including collimators, are placed adjacent to a surface of the subject to monitor and record emitted radiation. For three-dimensional reconstruction, the detector heads are rotated or indexed around the subject to monitor the emitted radiation from a plurality of directions. In SPECT, emission radiation is detected by each collimated detector. In PET, data collection is limited to emission radiation that is detected concurrently by a pair of oppositely disposed heads. The monitored radiation data from the multiplicity of directions is reconstructed into a three dimensional image representation of the radiopharmaceutical distribution within the subject.
One of the problems with these imaging techniques is that photon absorption and scatter by portions of the subject or subject support between the emitting radionuclide and the detector heads distort the resultant image. One solution for compensating for photon attenuation is to assume uniform photon attenuation throughout the subject. That is, the subject is assumed to be completely homogeneous in terms of radiation attenuation with no distinction made for bone, soft tissue, lung, etc. This enables attenuation estimates to be made based on the surface contour of the subject. However, human subjects do not cause uniform radiation attenuation, especially in the chest.
In order to obtain more accurate SPECT and PET radiation attenuation measurements, a direct transmission radiation attenuation measurement is made using transmission computed tomography techniques. More specifically, radiation is projected from a radiation source through the subject. Attenuated radiation rays are received by the detector at the opposite side. The source and detectors are rotated to collect transmission data concurrently or sequentially with the emission data through a multiplicity of angles. This transmission data is reconstructed into an image representation using conventional tomography algorithms. Regional radiation attenuation properties of the subject and the support, which are derived from the transmission computed tomography image, are used to correct or compensate for radiation attenuation in the emission data.
SPECT and PET measurements are typically made at incrementally stepped locations. One difficulty resides in optimizing the sampling of both the SPECT or PET emission data and the transmission data so as to reduce overall scan time. Typically, nuclear camera detector heads are stepped to a plurality of positions around the patient, e.g. 60 positions. At each position, emission and/or transmission radiation data is collected. The total time to perform a transmission scan is composed of the time to actually acquire data at each angular orientation and the time to mechanically rotate the gantry from one angular orientation to another and stabilize it at the new orientation. Typically, these two components are of a similar order of magnitude, e.g. 4-5 seconds for data collection at each angular orientation and approximately 2-4 seconds for gantry rotation to each angular orientation and stabilization. A wait time for stabilization of only 2-4 seconds per step adds 4-8 minutes to a 120 step scan.
The present invention contemplates a new and improved data sampling technique for collecting transmission radiation which overcomes the above-referenced problems and others.
In accordance with one aspect of the present invention, a method of diagnostic imaging using a nuclear medicine gamma camera includes placing a subject in a subject receiving aperture and injecting the subject with a radiopharmaceutical. At least one radiation source and a plurality of radiation detectors are positioned about the subject receiving aperture such that the radiation source is across the subject receiving aperture from a corresponding radiation detector. Radiation from the radiation source is transmitted toward the corresponding radiation detector which is positioned across the subject receiving aperture. The at least one radiation source and radiation detectors are continuously rotated together about the subject receiving aperture. Radiation transmitted by the radiation source is detected using one of the plurality of radiation detectors and reconstructed into an attenuation volume image representation. Radiation emitted by the injected radiopharmaceutical is detected using the plurality of radiation detectors and reconstructed into an image representation.
In accordance with another aspect of the present invention, a nuclear medicine gamma camera for diagnostic imaging includes a rotating gantry which defines a subject receiving aperture. A plurality of radiation detectors are movably attached to the rotating gantry such that the detector heads rotate about the subject receiving aperture with rotation of the rotating gantry about an axis of rotation. At least one radiation source is mounted to at least one detector head for rotation therewith such that transmission radiation from the radiation source is directed toward and received by a corresponding detector head positioned across the subject receiving aperture from the radiation source. The radiation source is rastered back and forth in a direction parallel to that of the axis of rotation. A raster sensor detects rastering of the radiation source across a field of view and a gantry sensor detects gantry rotation about the subject receiving aperture. A reconstruction processor reconstructs a volumetric emission image representation from the detected emission and transmission data, the sensed rastering of the radiation source, and the sensed gantry rotation.
In accordance with another aspect of the present invention, a method of generating emission radiation images includes concurrently (1) continuously rotating a radiation source around an axis of rotation and (2) rastering a radiation source back and forth parallel to the axis of rotation. Radiation transmitted from the radiation source and radiation emitted by radioisotopes disposed in a volume of interest adjacent the axis of rotation are detected in at least one detection plane which is parallel to and displaced from the axis of rotation. The at least one detection plane is rotated concurrently with the radiation source. The rastering of the radiation source is sensed as the transmitted radiation is detected and the rotation of the radiation source and the at least one detection plane are sensed as the transmitted and emitted radiation are detected. The detected transmission radiation is reconstructed into a transmission volume image representation. Detected emission radiation is weighted with the transmission image representation and the weighted emission radiation is then reconstructed into a volumetric emission radiation image representation.
One advantage of the present invention is that it reduces gantry dead time.
Another advantage of the present invention is that it reduces overall transmission scan time by approximately 50%.
Another advantage of the present invention is that it provides greater resolution for SPECT emission data than is required for transmission data.
Other benefits and advantages of the present invention will become apparent to those skilled in the art upon a reading and understanding of the preferred embodiment.